Electronic control circuit for a starting switch of a motor vehicle

ABSTRACT

An electronic control circuit for a motor vehicle starter contacter includes a management unit ( 26 ) having: 
         first means for detecting the open or closed state of the power contact ( 20 ),    and second means for regulating the power supply of the winding ( 18 ) during the starting cycle when the power contact ( 20 ) is still open after a predetermined period of time following commencement of the order for starting.        

     In order to obtain automatic elimination of any fault in the form of an insulation effect, due to dirt or to an insulating particle in the contact zone during the starting process, and to match the energy supplied to the contacter, the second means are so arranged as automatically to produce, during a period of time, a set of pulses which are delivered to the winding ( 18 ) in such a way as to reiterate actuation of the contacter ( 16 ) so long as the order for starting is maintained, and in order to modify the intensity of the power supplied to the winding ( 18 ) during the said period of time, or when the operator reiterates the demand for starting in the event of failure of the moving contact ( 20 ) to close.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an electronic control circuit for a startercontacter for a motor vehicle, the said contacter comprising a powercontact for supplying power to the electric motor of the starter, and atleast one excitation winding for actuating the power contact between anopen position and a closed position, the said control circuit includinga management unit having:

-   -   first means for detecting the open or closed state of the power        contact,    -   and second means for regulating the power supply to the winding        during the starting cycle when the power contact is still open        after a predetermined time after the commencement of the order        for starting.

STATE OF THE ART

With reference to FIG. 1, a motor vehicle starter 10 comprises anelectric motor 12 which is electrically connected to the positiveterminal 14A of a power supply battery, through an interposed powercontacter 16. The other terminal 14B of the battery 14, which is thenegative terminal, is connected to earth.

The contacter 16 comprises at least one excitation winding 18 foractuating a moving contact 20, which co-operates with fixed contacts 22,24 in such a way that, in normal operation, it occupies either an openposition when the winding 18 is not energised, or a closed position inthe case where the latter is being excited during starting of the motorvehicle. The fixed contact 22 of the contacter 16 is connected to theterminal 14A of the battery 14, while the other fixed contact 24 isconnected to the terminal 12A of the motor 12. The other terminal 12B ofthe motor 12 is connected to earth.

Excitation of the winding 18 of the contacter 16 is governed by anelectronic management unit 26, in the form particularly of amicroprocessor, which is automatically supplied with the batteryvoltage. The ignition key interrupter 28, or ignition switch, isconnected between the terminal 14A of the battery 14 and the controlunit 26, for initiating the starting process when it is actuated.

The management unit 26 takes note of the voltage at the terminals of thefixed contacts 22, 24 so as to verify whether the contacter 16 is in theopen or the closed state. The voltage is zero when the moving contact 20is closed, and is not zero when the moving contact 20 is open.

FIG. 2 shows the pattern, or law, for the power supply to the contacter,which is described in the document FR-A-2 795 884, and it shows thedevelopment of a cyclic ratio of power supply voltage to the winding fornormal operation of the contacter.

There may be many causes of failure of the moving contact 20 of thecontacter 16 to close. Apart from mechanical causes they may be linkedto the presence of non-conducting bodies at the surface of the contacts22, 24, 20, in particular dust, insulating particles, dirt, oxidationproducts, and so on. In that case, it is no longer possible to makeelectrical contact within the contacter 16. The latter is faulty and theengine is unable to start because the electric starter motor 12 cannotbe energised.

In the event of a malfunction of the contacter, holding the ignition keyfor too long a time in its starting position may give rise toover-heating of the contacter winding, or destruction of the powersupply transistor.

Electronic control units for starters offer various functions, amongwhich are the functions linked with:

-   -   displacement of the moving core and moving contact of the        contacter, and    -   operation of the contact of the contacter and of the associated        electric motor.

According to the document FR-A-2 795 884, to which reference may be madefor the structure of the starter, the management unit is capable ofgoverning the pattern of the power supplied to the excitation winding ofthe contacter so as to optimise displacement of the moving core as afunction of the displacement of the starter pinion. The cyclic ratio isapplied to the power transistor which is in series with the winding, thevalue of the said cyclic ratio being regulated by the management unit inresponse to the power supply voltage across the terminals of the starterand the resistance of the winding, which is dependent on temperature.

In the document FR-A-2 746 449, the management unit is capable ofdetecting whether the moving contact of the contacter is really closedor not, during the control phase. The excitation current of the controlwinding of the contacter is automatically interrupted or reduced whenthe moving contact of the contacter is still open at the end of apredetermined period of time after the commencement of the demandedpower supply. Such control of the excitation current of the contacterprevents damage to the control transistor or winding.

In the documents FR-A-2 760 891 and FR-A-2 760 910, the microprocessormanagement unit includes means for blocking the transistor whichsupplies power to the contacter winding, in response to the value of thedrop in voltage supply after the contacter has been closed.

The system thus goes into protected mode. In this kind of situation, theoperator will try again, and, because the pattern of power supply of thecontacter is unchanged, the system runs the risk of again remaining withthe contact open because of the presence of foreign bodies in thecontact gap.

OBJECT OF THE INVENTION

The object of the invention consists in providing a solution tomalfunctioning of the contacter of a motor vehicle starter, byautomatically eliminating any fault consisting of unwanted insulation orpollution of the contact zone during the starting process, and bymatching the energy supplied to the contacter.

According to the invention, the apparatus is characterised in that thesecond means are arranged to produce automatically, during a period oftime, a series of pulses delivered to the winding, in such a way as toreiterate activation of the contacter so long as the order for startingis maintained, and for modifying the intensity of the power supplied tothe winding during the said period of time, or when the operator repeatsthe demand for starting in the event of non-closure of the movingcontact of the contacter.

The power supply pulses for the winding act on the displacement of themoving core of the contacter, causing the moving contact to be propelledrapidly towards the fixed contacts. The repeated impact of the movingcontact on the fixed contacts generates mechanical shocks which arecapable of destroying any possible foreign body (such as dirt, oxidationproduct or insulating particles), and clean the contact zone of thecontacter.

According to a feature of the invention, the excitation pulses deliveredby the management unit comprise peaks having an adjustable cyclic ratio.

The management unit preferably has means for determining the cyclicratio of the power supplied to the winding as a function of variousparameters, in particular the temperature in the vicinity of thewinding, the number of commands for starting issued through the ignitionswitch, and the value of the voltage supplied to the terminals of thebattery or of the contacter in the open state.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features will appear more clearly from thefollowing description of one embodiment of the invention, which is givenby way of non-limiting example and is shown in the attached drawings, inwhich:

FIG. 1 is an electronic power supply circuit diagram for a contacter,for a motor vehicle in accordance with the state of the art;

FIG. 2 shows a known power supply pattern for the contacter representingthe development of a cyclic ratio of the power supply voltage for thewinding in normal operation of the contacter;

FIG. 3 consists of diagrams of various parameters in the event offailure of the contact to close on the first try, with governing of thecontacter in accordance with the invention;

FIG. 4 is a contacter control diagram in the event of failure to closeon the first try;

FIG. 5 shows a contacter power supply pattern in the event of failure ofthe contact to close.

DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to FIGS. 3 to 5, the invention is applicable to systemswhich make use of a unit for managing control of the commands to thecontacter, comprising power supply patterns to the winding 18 of thecontacter 16, and detection that the contact 20 is open after it hasbeen put into operation. During a malfunction of the starter in theevent of non-closure of the moving contact 20 of the contacter 16, dueto the presence of foreign bodies (such as dirt or particles), theinvention consists in:

-   -   firstly, reiterating the actuation of the contacter 16 by        repeated pulses, so long as the operator requires the starting        function and so long as the contact 20 is considered to be open,    -   and secondly, modifying the power supply patterns of the        contacter 16 during the operating mode described above, or when        the operator is repeating his demand for starting in a        predetermined period of time following failure of the contact 20        to close.

After activation of the control following closure of the interrupter 28(diagram A, FIG. 3), the control/command management unit 26 suppliespower to the winding 18 of the contacter in accordance with a particularpattern which conforms with the development of the cyclic ratio of FIG.2, as is described in the above mentioned document FR-A-2 795 884.

If the management unit 26 detects that the contact 20 has not closed(diagram B, FIG. 3), and if the command made by the ignition key 28 ismaintained, the system then automatically emits a salvo of pulses(diagram C, FIG. 3) to the winding 18 of the contacter 16, so long asthe contact 20 does not close. A thermal protection function may beadded to this mode of operation in the event that the contact 20 has notclosed.

There corresponds, to each power supply pulse of the winding 18, adisplacement of the moving core of the contacter 16 which causes themoving contact to be propelled rapidly towards the fixed contacts 22,24. In this way, the repeated impact of the moving contact 20 on thecontacts 22, 24 can destroy any foreign body (such as dirt, oxidationproduct or insulating particles), and to clean the contact zone of thecontacter 16. Thus, in diagram B, the contact closes and the winding 18is supplied with power continuously (diagram C) for excitation of themotor 12. Opening of the interrupter 28 and contact 20 occurs at a timeTn.

In FIG. 3, the width of a salvo of pulses (T1-T0) corresponds, by way ofexample, to 200 ms. The gap between two successive pulses (T2, T1) is 50ms. The total time (Tn-T0) between closure of the contact 20 and theinitial instant at which control by the ignition switch 28 is activated,is less than 30 seconds before thermal protection occurs.

In this circuitry, it is proposed to match the power supply of thewinding 18 as a function of parameters such as: temperature, the numberof operations carried out, and supply voltage. The system is capable incertain cases of providing all the power from the battery 14.

When the operator interrupts control of starting prematurely by openingthe ignition switch 28 during malfunctioning of the contacter 16, thepower pulses have not had time to close the contact 20 correctly. Oncethe operator repeats his command within a predefined period of time, themanagement unit 26 matches the power supply of the winding 18 as afunction of parameters such as: temperature, the number of operationscarried out, and supply voltage. The power supply pattern, or law, isthen modified in such a way that the system provides a sufficiently highlevel of energy to the moving core of the contacter 16 for the latter totransfer this energy to the moving contact 20, which will then violentlyimpact on the foreign bodies in the contact zone.

One example of a control law is to restore all of the power from thebattery 14 in the winding 18 of the contacter 16. In that case, thecyclic ratio of power supply voltage of FIG. 5 will be used, the cyclicratio being the ratio between the conduction time of the transistor (notshown) which is in series with the winding 18, and the total duration ofa cycle. The cyclic ratio R4 between the instants t5 and t6 is constant,and enables high intensity current to flow in the winding 18. The timeinterval t5-t6 is greater than the time interval t0-t1 of FIG. 2. Thecyclic ratio R5 beyond the instant t6 substantially corresponds to thecyclic ratio R3 in FIG. 2.

Such an operating cycle enables faults due to incidental contactinsulation (such as oxidation products, insulating dusts, dirt and soon) to be automatically eliminated and controlled, the operator nothaving to try doing anything about it.

1. An electronic control circuit for a starter contacter for a motorvehicle, the said contacter (16) comprising a power contact (20) forsupplying power to the electric motor (12) of the starter (10), and atleast one excitation winding (18) for actuating the power contact (20)between an open position and a closed position, the said control circuitincluding a management unit (26) having: first means for detecting theopen or closed state of the power contact (20), and second means forregulating the power supply to the winding (18) during the startingcycle when the power contact (20) is still open after a predeterminedtime after the commencement of the order for starting, characterised inthat the second means are arranged to produce automatically, during aperiod of time, a series of pulses delivered to the winding (18), insuch a way as to reiterate activation of the contacter (16) so long asthe order for starting is maintained, and for modifying the intensity ofthe power supplied to the winding (18) during the said period of time,or when the operator repeats the demand for starting in the event ofnon-closure of the moving contact (20).
 2. An electronic control circuitfor a contacter according to claim 1, characterised in that theexcitation pulses delivered by the management unit (26) comprise peakshaving an adjustable cyclic ratio.
 3. An electronic control circuit fora contacter according to claim 2, characterised in that the managementunit (26) has means for determining the cyclic ratio of the powersupplied to the winding (18) as a function of various parameters.
 4. Anelectronic control circuit for a contacter according to claim 3,characterised in that the said cyclic ratio depends on the temperaturein the vicinity of the winding (18).
 5. An electronic control circuitfor a contacter according to claim 3, characterised in that the saidcyclic ratio depends on the number of commands for starting issuedthrough the ignition switch (28).
 6. An electronic control circuit for acontacter according to claim 3, characterised in that the said cyclicratio depends on the value of the voltage supplied to the terminals ofthe battery (14) or of the contacter (16) in the open state.